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Whether you have a mastectomy or breast-conserving surgery (lumpectomy) for breast cancer, your doctors need to know whether the cancer has spread to the lymph nodes. Lymph node involvement increases the likelihood that cancer cells have spread through the bloodstream to other parts of the body. Women with some forms of very early breast cancer, such as ductal or lobular carcinoma in situ, do not need lymph node testing.

There are two ways for your doctor to check the lymph nodes under your arm. They are:

• Axillary lymph node dissection. During this surgery, 10 to 20 lymph nodes in the armpit are removed and checked for cancer cells.
• Sentinel lymph node biopsy. This is a procedure in which tissue is removed from the lymph node closest to the cancer—the sentinel node (SN) or group of nodes—to help find out whether breast cancer has spread to this area.

Removing lymph nodes from under the arm can sometimes cause lymphedema, a swelling in the arm.

In the past, doctors believed that removing as many lymph nodes as possible would improve chances for cure. But lymph node surgery itself does not improve your chances for a cure. Treatment with chemotherapy, hormone therapy, or targeted therapy offers the best chance of destroying cancer cells that have spread beyond the breast.